Electrophotographic printers, such as digital proofing and other printing machines produce single color or multicolored prints of an original document. A photoconductor film secured to a carrier member is first charged to a uniform potential to sensitize its imaging surface. The charged surface of the photoconductor film is exposed to an image of the original document, and records an electrostatic latent image corresponding to the informational areas contained within the image of the original document. The latent image is developed with liquid toners or inks. This imaging process may be repeated for each process color, with the images sequentially recorded on the photoconductor film. Typically, magenta, cyan, yellow, and black inks are the four standard colors, and additional special colors also may be used. The developed image is transferred from the photoconductor film to a print medium. Heat and pressure permanently transfer the image to the print medium to complete the process.
These apparatus, like other printers and copiers, require sheets of material, such as paper, to be fed individually from a stack in a tray to a downline location. Many different systems are used to grip and transport the first sheet from the tray to the downline location. Typically, these systems grip the sheets using vacuum grippers mounted on a bar and pivot from the tray to a downline location. However, none of these gripping and transporting systems have an integrated method, as part of the transport system, which prevents more than one sheet at a time from being fed to the downline location. Known systems require external devices to accomplish adhesion breaking. Such methods can include projecting air jets at the edge of the stack to separate the sheets, or using a relatively rough surface, such as a fixed coil spring, to scrape the edges of the sheets to separate the sheets. There is a need for a simple and inexpensive internal and integral method of transporting the sheets and breaking the adhesion between the first two sheets in a tray to prevent transporting more than one sheet at a time.